Complete the following table using the molarities you calculated for each buffer
ID: 883394 • Letter: C
Question
Complete the following table using the molarities you calculated for each buffer in Part 1. Using a 10 mL aliquot of the buffer, show the change in mmoles when 0.01 mL of 2.0M HCl is added to the buffer. Predict the change in pH after the addition.
Complete the following table using the molarities you calculated for each buffer in Part 1. Using a 10 mL aliquot of the buffer, show the change in mmoles when 0.01 mL of 2.0M NaOH is added to the buffer. Predict the change in pH after the addition.
mmol of Tris-HCl Post Addition of HCL
mmol of Tris Predicted pH Buffer 1 0.000175 7.5e-05
Buffer 2 0.0001875 6.25e-05
Buffer 3 0.00015 0.0001
Explanation / Answer
Henderson-Hasselbalch equation
For Tris base at room temperature pKa is 8.08
Molarity of HCl =
X= 0.0007292g of HCl = 0.00002
HCL will reduce the amount of Tris base and increase the amount of Tris-HCl
So, new moles of Tris base for Buffer 1
=0.000055 moles of Tris base
new moles of Tris-HCl for Buffer 1
0.000195 moles of Tris-HCl
For Buffer 1 predicted pH will be
pH = 8.08 +
Similarly for another
Buffer #
Initial moles of Tris-HCL
Initial moles of Tris
Post Addition of HCL
mmol of Tris-HCl
Post Addition of HCL
mmol of Tris
Predicted pH
Buffer 1
0.000175
0.195
0.055
7.530328
Buffer 2
0.0001875
6.25e-05
0.2075
0.0425
7.391371
Buffer 3
0.00015
0.0001
0.17
0.08
7.752641
So, new moles of Tris base for Buffer 1
new moles of Tris-HCl for Buffer 1
0.000155 moles of Tris-HCl
Moles of NaoH added 0.0008 mole
Buffer #
Initial moles of Tris-HCL
Initial moles of Tris
Post Addition of HCL
mmol of Tris-HCl
Post Addition of HCL
mmol of Tris
Predicted pH
Buffer 1
0.000175
0.000155
9.50E-05
7.867392
Buffer 2
0.0001875
6.25e-05
0.000168
8.25E-05
7.772439
Buffer 3
0.00015
0.0001
0.00013
1.20E-04
8.045238
Buffer #
Initial moles of Tris-HCL
Initial moles of Tris
Post Addition of HCL
mmol of Tris-HCl
Post Addition of HCL
mmol of Tris
Predicted pH
Buffer 1
0.000175
0.195
0.055
7.530328
Buffer 2
0.0001875
6.25e-05
0.2075
0.0425
7.391371
Buffer 3
0.00015
0.0001
0.17
0.08
7.752641